a) Field of the Invention
The invention is directed to a geodetic device according to the preamble of the first patent claim. This device is outfitted with a plummet or plumb bob oriented to the base point or ground point. It can be used for theodolites or for electronic tachymeters or simply as a plumb bob or as means for adjusting according to zenith and/or nadir points.
b) Description of the Prior Art
The simplest solution for centering the vertical spindle of a geodetic device over the center of a geodetic fixed point or ground point is the plumb bob which is attached to the device and oriented to the center of the ground point. The plumb line accuracy is poor and is only adequate for simple centering.
For purposes of centering a geodetic device, the markings have centers of a mechanical type such as points, bore holes, concentric circles, crosses chiseled in stone, or nails, etc. In order to increase centering accuracy over a ground point of this kind, optical plummets for theodolites and tachymeters are known.
A known optical plummet has a small folded or bent telescope which can be focussed and whose objective lens lies in the vertical spindle of the geodetic device, wherein its tube with the eyepiece is arranged vertical thereto in the support. The ground point is illuminated by an optical light beam and the deviation from the center can be determined through the cross-hair of the eyepiece and corrected corresponding to the position of the geodetic device over the ground point. However, an exact centering is highly dependent on the existing illumination conditions and on the quality and nature of the ground point.
In an arrangement described in DE 4 007 245 A1 and DE-GM 296 03 681.1 for geodetic devices, an illuminating visible laser diode pen serves to mark, by its illuminating spot, the perpendicular-falling light beam on the ground point. In this case, the observer need no longer look into the eyepiece, but can observe and assess the centering process by the displacement of the device on the tripod directly at the location with the naked eye. A disadvantage consists in that the laser spot is difficult to see on dark marks. Also, assessing the centering process from such a relatively great distance brings about a loss in accuracy. Further, the laser spot is difficult to see when the surroundings are very bright.
The Japanese Applications 5-71961 (A) and 6-129854 (A) disclose arrangements for leveling geodetic devices by which the adjustment in the horizontal plane is carried out by motor-actuated adjustment of the foot screws of the device. The motor driving means are controlled by signals of electronic levels.